Washington — Immigration has burst onto the Republican presidential campaign stage, with some candidates employing the scarlet “A” word – amnesty – to label the policy prescription of rivals. Others are using the issue to sound tough on national security.

But don’t expect to hear any comprehensive or politically realistic discussion of what for some crucial segments of the voting population remains an emotional topic, many immigration experts say.

Instead, they add, candidates will use such a hot-button issue as a vehicle for saying something else – about themselves or others. And some voters for whom the illegal-immigration issue resonates will in turn use what they hear to give a candidate a Roman thumbs up or thumbs down.

“It’s an issue that’s going to be around for the rest of the campaign, so get used to it popping up,” he adds. “It’s just not going to be a clarifying part of it.”

Jobs and the economy may be the overarching campaign issue, but for a core of conservative Republican primary voters, immigration constitutes a key test for defining who a candidate is. The downside of that, some conservative policy analysts say, is that it leads to one-upmanship among the candidates to see who can sound toughest.

“Immigration is a legitimate issue because we do have a problem with illegal immigration,” says Daniel Griswold of the Cato Institute in Washington.

“Unfortunately, we’re seeing a kind of demagogic tit for tat defined by the harshness of the rhetoric as each candidate tries to outdo the other,” he also says. “First it’s a fence all along the border, then it’s a two-tier fence, and that leads to an electrified two-tier fence that will electrocute any illegal who touches it.”

Some of the key words and phrases related to immigration that have been used by the Republican hopefuls in recent weeks include “humane,” “heart,” “law and order,” “deport,” and of course “amnesty.”

Former House Speaker Newt Gingrich jolted sleepy viewers to attention and fired up the blogosphere last week when he used a CNN debate on foreign policy to argue for a “humane” immigration policy. It would provide a path to legalization for illegal immigrants who have been in the United States for decades.

Mr. Gingrich has not backed off his proposal, but he has worked in subsequent days to shore up his anti-illegal-immigration credentials. He’s told audiences in South Carolina that he supports a state law that would require police who are suspicious about the status of a stopped driver to verify the driver’s immigration status with federal officials.

But it was Texas Gov. Rick Perry who first demonstrated the potency of the immigration issue in the GOP race – and the perils for Republican candidates who get it wrong.

Challenged at a September debate over his support for Texas’ version of the DREAM Act – which extends in-state tuition to college students who have been educated in state schools but who lack legal status – Governor Perry responded that anyone who didn’t support the idea doesn’t “have a heart.”

Down plummeted Perry’s formerly high-flying numbers. Since then, he has regularly outdone himself trying to reestablish his tough-on-illegals credentials – insisting that as president he would “shut down” the southern border and deport all illegal immigrants rounded up.

“My policy will be to detain and deport every illegal alien who is apprehended in this country,” Perry declared this week in New Hampshire. “And we’ll do it with an expedited hearing process so that millions of illegal aliens are not released into the general population with some hearing date down the road.”

Perry has also been campaigning with Sheriff Joe Arpaio at his side – the Arizona sheriff known for his anti-illegal-immigration exploits.

But “Sheriff Joe” is unlikely to be able to reverse Perry’s slide, immigration policy analysts say.

“You have to wonder how many New Hampshire primary voters even know who this sheriff from Arizona is, so it’s hard to see how he’s the guy who’s going to save [Perry],” says Stuart Anderson, executive director of the National Foundation for American Policy in Arlington, Va.

But Gingrich is unlikely to suffer the same fate as Perry over his immigration stance, says Mr. Anderson, who specializes in immigration issues. While Perry’s “heart” comment sounded like he was moralizing, he says, Gingrich’s “humane” comment – and the way he defined its application to illegal aliens who have lived in the US “for decades” – probably came off as common sense to many listeners, especially in the broader audience of Republicans and independents.

“We have to remember that about 70 percent of the illegal immigrant population came here 10 years ago or more,” Anderson says. “I think people make a distinction between being told they are morally wrong if they don’t support providing taxpayer-funded schooling for illegal immigrants, and being told that we’re going to have to find a way to address the legal status of people who have lived here for a long time.”

Given the pitfalls that immigration presents, Republican candidates might be better off steering clear of the issue altogether. But Mr. Krikorian of the Center for Immigration Studies says it won’t go away because enough voters stick to it as a defining issue.

“For the voters who are worried about things like the loss of America’s sovereignty, that we’ve lost control of our country, immigration resonates as an us-versus-them issue that identifies politicians who are post-American,” Krikorian says.

That’s why Perry fell so fast, he adds. “People who had assumed, ‘He’s one of us’ suddenly were saying, ‘Aha, he’s really one of them.’ And he hasn’t been able to recover from that.”